The invention discloses a method used for preparing sericite powder used for cosmetics. The method comprises following steps: shear flocculation, wherein a sericite quartz powder ore pulp with a mass concentration of 10 to 60% is delivered into a stirring sanding dispersing multifunction machine for shearing and stirring, and an inhibitor, a pH value regulating agent, a surface conditioning agent, and a cation collector are added successively so as to complete preliminary modification of sericite and formation of hydrophobic flocculation; flotation and purification, wherein after shear flocculation, the sericite quartz powder ore pulp is delivered into a flotation machine so as to obtain ore concentrate via floatation, wherein floatation concentration is controlled to be 3 to 20%, ore pulp pH value is controlled to be 2 to 3; and aging and modification, wherein obtained ore concentration I and II are subjected to dewatering and drying, and aging at high temperature so as to obtain the modified sericite powder used for cosmetics. The technological process of the method is coherent; operation is simple; the prepared cosmetic pigment is high in purity, excellent in dispersity, glossiness, malleability, and skin paste performance; skin feeling is fresh; the performance of the sericite powder is capable of satisfying quality requirements of extender pigments used for cosmetics; and the method can be used for matured industrialized large-scaled production.